This invention is related to the power generation industry and, more particularly, to the field of electrical power generators.
In the power generation industry, steam turbines are often used to generate electrical power. The steam turbines often are positioned in a series of varying steam pressures so that a high pressure (HP) turbine, an intermediate pressure (IP) turbine, and a low pressure (LP) turbine are respectively positioned one after the other. With reaction blading, the reaction of steam causes the blades of the rotor to turn. The reaction blading provides a very high pressure drop and, accordingly, the thrust across the rotor is quite high. Accordingly, an imbalance can arise between the HP turbine and the IP turbine and/or the LP turbine.
Although a split flow turbine can be used in an attempt to reduce or eliminate the thrust for the IP and/or combined IP-LP turbines, split flow turbine designs can be expensive and complex. Combined IP-LP turbines with a split flow design also have a thermal efficiency loss associated with the redirecting of the steam from the exit of the IP section of blading to the inlet of the LP section of blading. Accordingly, for certain applications, an IP turbine and/or a combined IP-LP turbine with reaction blading and a straight through flow configuration is desirable.
Therefore, as an alternative, a balance piston can be positioned at the inlet to the IP and/or combined IP-LP turbines having a straight flow design in an attempt to thereby balance thrust. Even with such a balance piston, however, the turbine system can still have problems in that creep deformation of the balance piston can occur. For example, in a large diameter balance piston positioned in such a turbine system, a large tangential stress in the rotor material can arise at running or operational speeds and due to the location of the balance piston near a hot inlet of the IP turbine, creep deformation can also occur.
In view of the foregoing, the present invention provides a steam cooling system and associated methods for a balance piston of a steam turbine system which allows a straight flow through design for each of a series of turbines in the system and which significantly reduces potential damage to the balance piston. The present invention also advantageously provides a steam cooling system and associated methods having cooling steam routed between a HP turbine and an IP-LP turbine to reduce potential damage to the balance piston. The present invention also advantageously provides a steam cooling system and associated methods having a straight through design for each of a series of turbines to thereby reduce the costs and complexity for the turbine system. The present invention further advantageously provides a steam cooling system and methods which significantly reduces or eliminates the efficiency losses of redirecting the steam that is found in a split flow combined IP-LP design.
More particularly, the present invention provides a steam cooling system having a first high pressure (HP) steam turbine having a straight through configuration, a second intermediate pressure (IP) steam turbine having a straight through configuration positioned adjacent the first HP steam turbine, and a balance piston positioned adjacent the inlet of the second IP steam turbine and between the second IP steam turbine and the first HP steam turbine. A steam cooling conduit is preferably positioned to have an inlet adjacent the first HP turbine and an outlet adjacent the balance piston for providing a steam cooling path therebetween. The system also has steam pressure controlling means connected to the conduit for controlling cooling steam pressure during cooling steam flow between the first HP turbine and the second IP turbine so that the cooling steam conduit pressure is operationally maintained at a predetermined level greater than the inlet pressure of the second IP turbine.
The steam pressure controlling means preferably includes a controller positioned to control cooling steam pressure, a cooling steam control valve connected to the conduit and the controller, a first pressure sensor in communication with the controller and positioned adjacent the inlet of the IP turbine and downstream from the balance piston for sensing inlet pressure to the IP turbine, and a second pressure sensor positioned in communication with the controller in the conduit upstream from the first pressure sensor and the balance piston and downstream from the cooling steam control valve for sensing conduit cooling steam pressure so that the cooling steam control valve operationally opens and closes to maintain the cooling steam conduit pressure at a predetermined level greater than the inlet pressure of the second IP turbine.
The present invention also includes a method of steam cooling a turbine system. The method preferably includes positioning a balance piston between first and second steam turbines and adjacent the inlet of the second steam turbine, providing a steam cooling path between the first and second steam turbines and in communication with the balance piston, and controlling cooling steam pressure during cooling steam flow between the first and second steam turbines so that the cooling steam conduit pressure is operationally maintained at a predetermined level greater than the inlet pressure of the second steam turbine.